The present invention relates generally to wireless data networks. More particularly, the present invention relates to adaptive multiple access techniques for wireless networks.
In typical wireless networks, the wireless network devices use a common frequency band, and so must employ mechanisms to share the band. The most common sharing scheme is specified by the IEEE 802.11 standard, and is referred to as Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). According to CSMA/CA, a wireless network device monitors the band to determine whether other devices are transmitting. If no such transmissions are sensed, the wireless network device applies a back-off scheme then begins its intended transmission.
On receiving the packet without error, the recipient sends an acknowledgement (ACK) packet. If the wireless network device receives the ACK packet without error, the wireless network device begins its next transmission by monitoring the band again to determine whether other devices are transmitting.
However, if the wireless network device does not receive an ACK packet, or receives an ACK packet with errors, for example due to a collision with another station attempting to transmit on the band at the same time, the wireless network device waits for a random back-off interval and then re-sends the packet. Subsequent collisions require substantially longer back-off intervals.
The main disadvantage of CSMA/CA is that the back-off interval becomes longer, especially as the number of wireless devices in the wireless network increases, causing more collisions and reducing the performance of the wireless network.